Structural studies of cytochrome b562 from E. coli. The structure of cytochrome b562 from E. coli will be studied by x-ray diffraction methods. Both the oxidized and reduced protein will be examined. The major goal will be to understand the mechanism of electron transport at the molecular level and to apply this understanding to other systems, such as the insoluble b cytochromes of mitochondria. A second objective is to compare its structure to other heme proteins of known structure such as cytochrome b5, cytochrome c and hemoglobin. Ferricytochrome b562 crystallizes in a triclinic unit cell with two molecules per asymmetric unit. The crystals are suitable for x-ray analysis and the data can be measured to 2.0 A resolution. Crystals of ferrocytochrome b562 are isomorphous and display intensity changes when compared with the oxidized protein. The location of the two independent iron atoms in the unit cell have been obtained from the anomalous dispersion difference Patterson. The relative orientation of the two molecules has been determined from the Rossmann rotation function. One heavy atom derivative has been solved and several others are being studied. X-ray phases based on the isomorphous derivatives and the molecular replacement method have been used to calculate an electron density map at 4.5A resolution. Extension of the data to higher resolution and including more derivatives is in progress.